Data Sufficiency

There are lots of information in the table. but most of them are to distract us.

Question stem ask : What was the number of voters who responded "favorable" for both candidates?

(1) The number of voters who did not respond "Favorable" for either candidate was 40.

That means the other 60 voters responded 'Favorable' for at least one candidate.

working on only favorable , we get :
60 = 30 + 40 - Both
Both = 10. sufficient